The proliferation of two native brown algae, Turbinaria ornata and Sargassum pacificum, was observed on high islands of French Polynesia since the early 1980s. High swells frequently remove algae from their substratum, floating algae concentrate due to local currents in specific lagoon locations, and large compact rafts eventually form. A study of the prospective industrial use of drifting algae was conducted, including estimates of biomass, biomass renewal and agronomical trials. Harvesting rafts could efficiently limit the geographic expansion of proliferating populations and their associated nuisance. The drifting biomass in rafts around Moorea Island was estimated at 13,062 +/- 1,998 kg dry mass based on aerial photographs acquired on 31 August 1997. To measure the renewal rate and temporal variation of the raft biomass, we completely harvested one of the larger rafts in February 2002, which was quickly renewed within 10 days. In situ and airborne assessments of biomass show a range of variation between 178 kg and 8.5 t of dry algae. Steady resource availability is required for industrial exploitation, and we demonstrate that drifting algae represent a valuable and significant renewable resource for French Polynesia. Moreover, agronomical enrichment trials using drifting algae as organic additives gave promising perspectives for agriculture uses, with an increase in size, dry mass and root development for maize plants.